This invention relates to control devices for controlling the temperature, humidity, and/or other environmental conditions in an interior comfort space, and is more particularly concerned with an improvement to a wall thermostat to prevent inaccuracies and misoperation that may result from intrusion air which may enter the thermostat from a hollow wall on which the thermostat is mounted.
Wall thermostats are typically installed on an interior wall of a house or other building to control the operation of a furnace, air conditioner, heat pump, or other environmental control equipment. The thermostat is intended to monitor the temperature of the room or other interior comfort space continuously, and to adjust the operation of the associated environmental control equipment to keep the interior comfort space parameter (e.g., temperature) within some range (e.g., 68° F., ±1.0° F.). Other controls may be sensitive to other parameters, such as humidity or particulate level. The thermostat is connected to the furnace, air conditioner, heat pump or the like by means of a run of thermostat wires, which pass from the furnace control board up through spaces in the interior walls, and emerge at an opening in one of the walls, and this is the place the thermostat is to be mounted. An opening is provided in the back of the thermostat for the wires to pass through, so that the wires can be connected to appropriate contacts inside the thermostat housing.
In practice, the opening or penetration in the wall for the thermostat wires allows some intrusion air to enter the room, and this air passes out of the wall cavity, through the thermostat opening, into the interior of the thermostat housing. As a result, the sensors inside the housing are influenced to a significant degree by intrusion air that comes through the hollow wall, and this air can be warmer or cooler than the rest of the air in the room. Even if a contractor plasters or caulks the wire opening during construction of the house, the plaster or caulk can eventually dry and crack, and permit intrusion air to enter the thermostat. As a result, the actual room air temperature (or humidity) can be outside the range set on the thermostat (or humidistat), and this can occur without any malfunction of either the thermostat or the environmental control equipment.
In addition, accurate control over room temperature is made difficult when the thermostat housing is in direct contact with the wall, which may be significantly warmer or cooler than the room air. That is, if the thermostat is in direct thermal contact with the wall, and if the wall is warmer or cooler than the air in the room, the accuracy of the thermostat can be impaired, even in the absence of intrusion air from the wall cavity. However, no one to date has considered thermally isolating the thermostat from the surface of the wall.